1. Field of the Invention
This invention relates to direct method of iron manufacture which comprises subjecting heavy oil to thermal cracking in a fluidized bed of iron ore particles as a fluid medium to recover light oil distillates thereby to convert the heavy oil toward declining in demand to light oil in a great demand and at the same time, reducing iron ore by reducing agent of a carbonaceous material, i.e. petroleum coke deposited as by-product on the surface of the iron ore upon cracking to produce reduced iron. More particularly, it relates to a method of producing reduced iron and light oil from iron ore and heavy oil wherein petroleum coke deposited on the iron ore undergoes gasification in a fluidized bed by an excessive amount of steam and a small amount of oxygen to obtain high-concentration hydrogen gas.
2. Description of the Related Art
Nowadays, the balance of supply and demand of petroleum products is in the situation that global trend of supply is toward heavy-gravity crude oil, and hence yield of heavy oil from crude oil is increasing year by year. Conversely, owing to skyrocketing rise in petroleum price conversion from petroleum to coal and LNG has been encouraged and particularly, the conversion into coal and LNG has been positively promoted in a fuel field easily susceptible of conversion into coal and LNG, namely, in a major consumption field of fuel oil such as iron and steel, cement, electric power, etc. and consequently, the demand for heavy oil tends toward decrease remarkably. On the other hand, with a light oil such as kerosene, gas oil, its demand tends toward expanding steadily both in civil use and industrial use in spite of the fact that its yield from crude oil is on the decrease. As a consequence, the demand-and-supply balance of petroleum products has a tendency toward oversupply of heavy oil and supply shortage of middle distillates such as kerosene, gas oil, etc. The gap between demand and supply of them is estimated to amount to twenty million kl/year in 1990. For this reason, an urgent important problem is to obviate the supply-and-demand gap by converting the surplus heavy oil into light oil. This problem is true not only in our country, but throughout the world.
As regards reduced iron, the demand of it is expected to be active mainly in developing countries and reduced iron plants are still now being constructed in succession mostly in petroleum producing countries. However, these plants for the production of reduced iron utilize natural gas as a source of reducing agent, and hence, their location is inevitably limited to natural gas producing districts.
A direct reduction method of iron manufacture is advantageous in that scale merits are not pursued unlike blast furnace iron manufacture method. Accordingly, the direct reduction method is economically practical as a small-scale ironworks even in such districts that market scale is small and it is inconvenient to transport products. However, in the present situation where natural gas is used as a reducing agent, the foregoing advantage inherent in the direct reduction method for iron manufacture is not sufficiently exhibited.
In view of the foregoing problems, in order to solve simultaneously both the problem of demand-and-supply gap of petroleum products and the problem of location of reduced iron plants as described above, the present invention is designed for utilizing heavy oil having a worldwide tendency toward oversupply as a source of reducing agent for the production of reduced iron and at the same time, for producing light oil, e.g., kerosene, gas oil, having a global tendency to supply shortage by submitting heavy oil to thermal cracking.
On the other hand, gasification technology for converting solid energy such as hydrocarbons or carbonaceous materials, e.g., petroleum coke into gaseous state which is easy to use has been investigated for many years in many countries, and several gasification furnaces were put into practice.
Then, in an era when petroleum resources are available in abundance, however, the gasification technology as a fuel technology has nearly lost its significance and only a few gasification furnaces still remain on stream.
In the latter half of 1970s, the petroleum oil crisis has struck a serious blow at the entire world economy and gasification technology of coal, coke, etc. again came to prominence. On the other hand, demand for heavy oil such as fuel oil which have been a cheap energy source and consumed in large quantities has declined rapidly, and the trend toward light oil including middle oil and light oil is predominating among petroleum products. Heavy oil is therefore directed at recovering middle and light oils by cracking. One such recovery methods is thermal cracking process which is widely practiced. Carbonaceous material or petroleum coke which is produced by thermal cracking from heavy oil is of little utility value where the material contains a substantial amount of sulfur ingredient in it, and effective utilization of petroleum coke present in an amount of 10-20% in heavy oil has been desired.
This invention has been accomplished to meet technological and economic requirements as described above.
A primary object of this invention is therefore to provide a new process of producing reduced iron and light oil from iron ore and heavy oil as raw material which process comprises a combination of: a step of subjecting heavy oil to thermal cracking in thermal medium of iron ore to recover light oil fractions and to deposit coke produced as a by-product on the iron ore surface, a step of gasifying the coke thus deposited with steam and oxygen to make a reducing gas including CO and H.sub.2, and a step of reducing the iron ore by the reducing gas to produce reduced iron (This process will be hereinbelow simple referred to as the KKI process.).
A particular object of this invention is, in the KKI process above, to produce a reducing gas necessary for reduction of iron ore by gasification of coke.
Another particular object is, in the KKI process, to adjust, during a gasification step, the amount of coke deposited on the iron ore upon thermal cracking to an amount suitable for subsequent reduction step by oxidization of it.
A further particular object is, in the KKI process, to supply the reduction step with heat by feeding the coke-deposited iron ore which is heated by heat evolution due to oxidation of the coke.
Another primary object of this invention is, in the KKI process, to obtain high-concentration hydrogen gas by putting the coke-deposited iron ore in contact with an oxidizing gas containing an excessive amount of steam, in the gasification step.